Using libzookeeper-mt-dev-3.3.5, on Ubuntu 12.04, the header files exist
under /usr/include/zookeeper.
Also, In ZooKeeper 3.4.0 and later, the header files will exist under
INCDIR/zookeeper, instead of INCDIR/c-client-src.
https://issues.apache.org/jira/browse/ZOOKEEPER-1033